The present invention relates to a blown boundary layer control system for a jet aircraft. More particularly, the invention relates to a system for safeguarding a jet aircraft against performance and operational penalties due to boundary layer separation.
Air breathing propulsion systems for jet aircraft must be designed to allow adequate quantities of appropriate quality air flow to the engine. Aircraft having a broad range of mission requirements may need variable inlets, and sometimes auxiliary inlets as well, to meet these requirements. Thus, for example, variable position cowl lips have been employed to align local inlet and free-stream flow during high angle of attack operation. Auxiliary inlets sized in excess of 50% of the main inlet are frequently necessary to provide efficient low speed performance. Furthermore, drag-producing boundary layer diverters, which plow thick approach surface boundary layer aside the inlet, are used to preclude low energy ingestion.
In the past, whenever these design approaches were not adequate to meet performance requirements, engine control modifications were invoked in an effort to achieve some degree of relief, perhaps as a trade against performance in some less important operating mode. More importantly, when these approaches were not adequate to match the inlet and engine's stability margins, that is, when frequent engine surge was a problem, engine surge margin was increased by bleeding compressor flow, thus trading away performance at a primarily important condition. This after-the-fact approach is always very expensive and can jeopardize the effort.
At the aft end of the propulsion system, shock-boundary layer induced separation on nozzle afterbodies, especially during transonic flight, can cause strong buffeting, leading to poor flying qualities and structural fatigue. Previously, this problem was not frequently encountered, because the high afterbody pressures induced by afterburning nozzles precluded local transonic flow. This problem will, however, become more frequent with advanced, higher thrust loaded aircraft that are more capable of transonic flight without the need for afterburning nozzles.
There are integrated inlet-engine systems flying, such as in the A-11 and Concord supersonic cruise aircraft, but those systems do not address boundary layer control issues with the minimal impact of the present invention. Low speed maximum power operation of those aircraft, for example, requires the weight, performance, reliability and complexity penalties of variable inlet geometry, while the present design employs relatively simple, small blowing jets. The relatively obscure visibility of the blown jet system makes it an ideal candidate for low observable aircraft.
The principal object of the invention is to provide a blown boundary layer control system for a jet aircraft, which system functions efficiently, effectively and reliably to safeguard against performance and operational penalties due to boundary layer separation.
An object of the invention is to provide a blown boundary layer control system for a jet aircraft, which system safeguards inlet-engine operating conditions.
Another object of the invention is to provide a blown boundary layer control system for a jet aircraft, which system supplies high pressure compressor air to a plurality of boundary layer control sites of potential propulsion system degradation.
Still another object of the invention is to provide a blown boundary layer control system for a jet aircraft, which system provides adequate quantities of appropriate quality air flow to an engine of the aircraft.
Yet another object of the invention is to provide a blown boundary layer control system for a jet aircraft, which system is devoid of drag-producing boundary layer diverters.
Another object of the invention is to provide a blown boundary layer control system for a jet aircraft, which system does not involve bleeding large amounts of compressor flow to provide increased surge margin.
Still another object of the invention is to provide a blown boundary layer control system for a jet aircraft, which system tailors the engine compression system to minimize performance degradation from compressor bleed.
Yet another object of the invention is to provide a blown boundary layer control system for a jet aircraft, which system precludes requirements for auxiliary inlets, high angle of attack devices and large boundary layer diverters and reduces or eliminates separated afterbody flow.
Another object of the invention is to provide a blown boundary layer control system for a jet aircraft, which system avails optimization of the trade of propulsion system performance for engine surge margin.
Still another object of the invention is to provide a blown boundary layer control system for a jet aircraft, which system minimizes or eliminates boundary layer separation and thereby provides maximized propulsion system performance and operational limits.
Yet another object of the invention is to provide a blown boundary layer control system for a jet aircraft, which system provides a synergistic relationship between the engine and the airframe, wherein engine-developed energy is used to enhance engine performance by improving inlet and afterbody performance.